What is a Condensate Pump?
A condensate pump
is a specific type of pump used to pump the condensate (water) produced in an HVAC (heating or cooling) or refrigeration system. They may be used to pump the condensate produced from latent water vapor in any of the following gas mixtures:
- Conditioned (cooled) building air
- Refrigerated air in cooling and freezing systems
- Steam in heat exchangers and radiators
- The exhaust stream of very-high-efficiency furnaces
- Condensate run-off from a Humidifier
Construction and Operation
as used in hydronic systems are usually electrically-powered centrifugal pumps. As used in homes and individual heat exchangers, they are often small and rated at a fraction of a horsepower, but in commercial applications they range in size up to many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. Large industrial pumps may also serve as the feedwater pump for returning the condensate under pressure to a boiler.
Condensate pumps usually run intermittently and have a tank in which condensate can accumulate. Eventually, the accumulating liquid raises a float switch energizing the pump. The pump then runs until the level of liquid in the tank is substantially lowered. Some pumps contain a two-stage switch. As liquid rises to the trigger point of the first stage, the pump is activated. If the liquid continues to rise (perhaps because the pump has failed or its discharge is blocked), the second stage will be triggered. This stage may switch off the HVAC equipment (preventing the production of further condensate), trigger an alarm, or both.
Small pumps have tanks that range from 2 to 4 litres (0.5 to 1 gallon) and are usually supported using the flanges on their tanks or simply placed upon the floor. A plastic impeller in a molded volute at the bottom of the pump provides the pumping action; this impeller is connected to the motor via a metal shaft that extends downwards from the motor mounted above the tank's top. Large pumps are usually pad-mounted drawing liquid from a tank (sump) below the floor. The smallest pumps may have no tank at all and are simply placed within a container such as the drip pan of a dehumidifier appliance.
The Pump Output
The output of small condensate pumps is usually routed to a sewer, drain, or the outside world via PVCl plastic tubing. If the outlet of the line is at a higher level than the tank of the pump, a check valve is often fitted at the outlet of the pump so that liquid cannot flow backwards into the pump's tank. If the outlet is below the tank level, siphonage usually naturally clears the output line of all liquid when the pump is deenergized. In cold regions of the world, it is important that condensate lines that are exhausted outside be carefully designed so that no water can remain in the line to freeze up; this would block the line from further operation.
Condensate is not pure water. If it is being condensed from an air stream, it may have dust, microbes, or other contaminants in it. If it is condensed from steam, it may have traces of the various boiler water treatment chemicals. And if it is condensed from furnace exhaust gases, it may be acidic, containing sulfuric acid or nitric acid as a result of sulfur and nitrogen dioxides in the exhaust gas stream. Steam and exhaust condensate is usually hot. These various factors may combine (along with local regulations) to require careful handling or even treatment of the condensate and condensate pumps used for these services must be appropriately designed.
Reading a Pump Curve
A pump curve tells you the flow performance of a pump relative to the head pressure. This is usually measured in gallons per hour or liters per hour, though sometimes condensate pump performance is rated in pints per hour. To read a pump curve, you must first examine the units of measurement used along each of the displayed axes. The pictured pump curve displays head pressure in Feet (along the left-side y-axis) and in Meters (along the right-side y-axis). Increased head pressure is indicated as you travel up the y-axis. The flow performance is indicated in gallons per hour (along the lower x-axis) and liters per hour (along the upper x-axis). This is an indication of the output flow of a pump.
The pump curve is read by first determining the head pressure of the application in which the pump will be used. Once you’ve determined your head pressure, simply follow the head value you have selected from the y-axis horizontally to where it intersects with the pump curve line. From that point, move vertically to the flow measurement on the x-axis.
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